Thursday, November 29, 2012

Improving hurricane intensity predictions

A bit of hurricane folklore has it that hurricanes have a dry side and a wet side - that is, whether you'll get more wind than rain when a hurricane passes through depends on which side of the center you're on. A new report from the NASA Jet Propulsion Lab points out that not only is this folklore true, it may to improve the ability to predict the intensity of hurricanes.

The researchers found the hurricanes that rapidly intensified tended to
exist within a moister large-scale environment than weaker storms. The
rapidly intensifying hurricanes had statistically significant higher
relative-humidity levels in their environments than storms whose
intensity was weakening or unchanged.

. . .

The team found substantial differences in relative-humidity levels
between storm quadrants. One factor may be the shape of the Atlantic
basin. Hurricanes in the Atlantic usually travel to the west or
northwest -- regions that are drier, climatologically-speaking, than
from where the storms originated. This causes the front two quadrants of
Atlantic hurricanes to be drier than their rear two quadrants.

A unique result the team found is that in their front-right quadrants,
rapidly intensifying hurricanes tended to have sharply higher amounts of
upper tropospheric moisture near their centers than they did farther
from their centers.

A previous post linking to some good explanations of why predicting hurricane intensity is so complex is here. NASA is "exploring collaborations" that will allow forecasters to incorporate relative humidity data into hurricane prediction system, so we may be able to see test data in the next few years.